KidBlog - safe and simple blogs for your students. The teacher creates the class, adds students, and controls the comments that are posted by students.

Lino - a Web 2.0 bulletin board where you can post notes, pictures, and videos. You can create different boards and share boards with other users. maintain your board on a computer or an app for an iPad, iPhone, or android.

PollEverywhere - Create online polls that students can participate in using their own devices. Responses can be given via text or through the Internet.

Socrative - Socrative is a smart student response system that empowers teachers to engage
their classrooms through a series of educational exercises and games via
smartphones, laptops, and tablets.

StudyBlue - Teachers and/or students can create their own flash cards via the website or the device app to study vocabulary and terms.

TodaysMeet - Create a classroom back channel (chat) where students can post questions as they think of them during a lesson. Or, use this for students to participate in a class discussion.

Wordnik - a dictionary that gives definitions from multiple sources. for many of the words, there are also pictures to give visual meaning as well.